1. Field of the Invention
The invention relates to a device and a method for the optical measurement of an optical system, in particular an optical imaging system, having one or more object-side test optics components to be arranged in front of the optical system to be measured, and/or one or more image-side test optics components to be arranged behind the optical system to be measured, to a container which can be used for such a device, and to a microlithography projection exposure machine equipped with such a device. The designations “object-side” and “image-side” indicate, in the way they are used specifically in the case of optical imaging systems, that the relevant test optics component is intended for positioning in the beam path of a used measuring radiation in front or, respectively, behind the optical system to be measured.
2. Description of the Related Art
Such devices and methods are known in various forms, in particular for measuring optical imaging systems with regard to aberrations. One field of application is the highly accurate determination of aberrations of high-aperture imaging systems such as are used, for example, in microlithography systems for patterning semiconductor components by means of the so-called wavefront detection using shearing interferometry, point diffraction interferometry and other known types of interferometer such as the Ronchi type and Twyman-Green type, or by means of Moiré measuring techniques. In most cases of these techniques, a periodic or wavefront-forming structure is arranged on the object side and imaged by the optical imaging system to be measured, and brought into superimposition or interference with the periodic structure provided on the image side. The interference or superimposition pattern produced can be recorded with the aid of a suitable detector and evaluated in order to adjust and/or qualify the optical imaging system. When the same radiation, for example UV radiation, is used for wavefront measurement as is used by the optical imaging system in its normal operation, it being possible for the measuring device to be integrated in one component with the imaging system, this is also denoted as a so-called system or operational interferometer (OI). A device of this type is disclosed, for example, in laid-open publication DE 101 09 929 A1.
Various methods are known in the literature for increasing the resolution of an optical imaging system, such as reducing the wavelength of the light used in the imaging, and increasing the image-side numerical aperture of the imaging system. The latter is achieved in so-called immersion objectives by using an immersion fluid: see, for example, the projection exposure machines operating with immersion as disclosed in laid-open publications JP 10303114 A and JP 12058436 A.
On the basis of shearing interferometry, such an OI device usually comprises an illuminating mask, also termed coherence mask, and an upstream illuminating optics on the object side, that is to say on the object side of the optical system to be measured, also denoted below as OUT (object under test). Adjoining the OUT on the image side is a diffraction grating, followed by a detector element such as a CCD array, with the optional interposition of imaging optics which project the exit pupil of the OUT onto the detector plane of the detector element. It is mostly the case that the coherence mask is arranged in the object plane, and the diffraction grating is arranged in the image plane of the OUT. In accordance with the spacing conditions to be observed for the optical beam guidance, there are respective interspaces between the object-side last test optics component of the measuring device and the OUT, between the OUT and the image-side first test optics component of the measuring device, and/or between respectively consecutive test optics components on the object side and/or the image side of the OUT.
These interspaces are customarily either open, that is to say in the interspaces the radiation used traverses an atmosphere which corresponds to that of the system neighbourhood, for example air, nitrogen or a vacuum atmosphere, or closed, and are operated or purged with the aid of a prescribed gas atmosphere.
Under these conditions, it is normally possible to use such measuring devices to measure imaging systems up to numerical apertures of the order of magnitude of 0.95. The measurement of objectives of higher numerical aperture of the order of magnitude of 1.0 and above, as in the case of objectives which are used in immersion and near-field lithography, is therefore scarcely possible.
A primary technical problem underlying the invention is to provide a device of the type mentioned at the beginning which, with relatively low outlay, permits even optical imaging systems of very high numerical aperture to be measured, and can be of relatively compact design, to provide a corresponding method and a container suitable for use in such a device, and to provide a microlithography projection exposure machine equipped with such a device.